if you are just wanting a formula, then used a nested if:
=If(A1="",(B1+ C1) - D1,If(B1="",(D1 + A1) - C1,....
Does that help?

Charles
edwinvon wrote:
I have 4 values - Rate, Index, Margin & Teaser. If I have 3 of the four I can
solve for any of them when they are missing. How do I create this to allow
input of values to solve for the missing value regardless of which one is
missing? 'Teaser= (Index + Margin)-rate', Index=(rate + Teaser) - Margin, and
Margin= (Rate + Teaser) - Index'